1. Field of the Invention
This invention relates to a stepping motor controller, more particularly, it relates to a stepping motor controller that enables automatic setting of a current set value for a stepping motor of a constant current control type.
2. Description of the Prior Art
A stepping motor controller being currently used comprises an excitation signal generator, a switching circuit, a winding of the stepping motor, a PWM (Pulse Width Modulation) constant current control circuit, a current sensor and a current setting circuit.
The excitation signal generator receives input pulse signals and generates excitation signals for controlling excitation sequence for the winding of the stepping motor. The switching circuit comprising a plurality of switching devices receives the excitation signals and controls the current in the winding. The PWM constant current control circuit controls the current in the switching circuit to be a predetermined set value. The current sensor detects the current flowing through the winding of the stepping motor. The current setting circuit is connected to a current setting terminal of the PWM constant current control circuit to set the current set value in the PWM constant current control circuit.
In general, the current setting circuit comprises a voltage divider comprising a fixed resistance and a variable resistance connected in series between a power source VM and the ground. The output voltage of the voltage divider is connected to the current value setting terminal of the PWM constant current control circuit.
In general, a stepping motor comprises a plurality of windings. However, since the stepping motor controller of the present invention can be composed of a single winding in the stepping motor, the following description will be made referring to only the single winding in the stepping motor.
The switching circuit that controls one of the windings of the stepping motor comprises a plurality of switching devices consisting of, for example, first, second, third and fourth switching devices. Collectors of the first and the third switching devices are connected in series. Likewise, collectors of the second and the fourth switching devices are connected in series. One end of the winding is connected to a node of the collectors of the first and the third switching devices, whereas another end of the winding is connected to a node of the collectors of the second and the fourth switching devices. Emitters of the first and the second switching devices are connected to the power source VM. Emitters of the third and the fourth switching devices are grounded through the current sensor.
The PWM constant current control circuit receives an output of the current sensor and transmits a control signal to the excitation signal generator to make a current in the switching circuit be the current set value set by the current setting circuit.
The excitation signal generator transmits excitation signals to the corresponding bases of the switching devices each time when an input pulse signal arrives to make a pair of switching devices comprising the first and the fourth switching devices, or another pair of switching devices comprising the second and the third switching devices, of the switching circuit, alternately become xe2x80x9conxe2x80x9d state and to make the current flowing through the winding become the set value mentioned above.
Thus, when the first pulse signal arrives at the excitation signal generator, the first and the fourth switching devices become xe2x80x9conxe2x80x9d state, and the current flows through the winding from its one end connected to the first switching device into another end connected to the fourth switching device. Further, when the second pulse signal arrives at the excitation signal generator, the first and the fourth switching devices become xe2x80x9coffxe2x80x9d state, the second and the third switching devices become xe2x80x9conxe2x80x9d state, and the current flows through the winding from its another end connected to the second switching device in to the one end connected to the third switching device. Thus, the stepping motor is driven by the current reversing its flow direction each time when a pulse signal arrives.
The current flowing through the winding is detected by the current sensor, then transmitted to the PWM constant current control circuit, where the current is controlled to be the current set value set by the current setting circuit.
In the stepping motor controller as stated above, the current set value of the PWM constant current control circuit needs to be adjusted so as to be in conformity with the specification (resistance) of the winding of the motor to be used, since the specification (resistance) of the winding of the motor differs according to the uses.
Heretofore, the current set value is set by a user handling individually the variable resistance of the current setting circuit according to the specification (resistance) of the winding of the motor to be used.
In case that the current set value is set manually by a user, it sometimes occurs that the set value may not be set correctly enough, and accordingly, the stepping motor may not exhibit its performance as expected, or the stepping motor may be overheated.
The object of the present invention is to provide a stepping motor controller that automatically detects specification of a stepping motor with a different winding specification (resistance), automatically sets a current set value for a PWM constant current control circuit corresponding to the winding specification (resistance) of the stepping motor, and enables to perfectly eliminate manual setting of the current set value.
According to the present invention to achieve the above object, a stepping motor controller comprising;
an excitation signal generator which receives input pulse signals and generates excitation signals for controlling excitation sequence for a winding of a stepping motor,
a switching circuit that receives the excitation signals and controls the excitation sequence for the winding of the stepping motor by a plurality of switching devices,
a PWM constant current control circuit for controlling current flowing through the switching circuit to be a predetermined current set value, and
a current sensor for detecting current flowing through the winding,
characterized in that the stepping motor controller further comprises a motor detector portion comprising;
a motor detector circuit that transmits a control signal for generating a constant current for a predetermined time for detecting the motor,
a constant current generator that receives the control signal and generates the constant current to be supplied to the winding,
a reference voltage generator that generates a reference voltage,
a voltage comparator circuit that compares the reference voltage with a voltage drop at the winding, and
a current value setting signal generator circuit that transforms an output of the voltage comparator circuit into a current value setting signal for the PWM constant current control circuit,
wherein an output of the current value setting signal generator circuit is connected to a current value setting terminal of the PWM constant current control circuit, is provided.
In the stepping motor controller according to the present invention, the constant current generator supplies the constant current to the winding, then the voltage comparator circuit compares the reference voltage with a voltage drop at the winding, and then the current value setting signal generator circuit transforms the reference voltage corresponding to the voltage drop at the winding into the current value setting signal for the PWM constant current control circuit, and the current value setting signal is supplied to the current value setting terminal of the PWM constant current control circuit. Accordingly, specification of a different stepping motor with a different winding specification (resistance) can be automatically detected, the current set value of the PWM constant current control circuit can be automatically set corresponding to the specification (resistance) of the stepping motor, and manual setting of the current set value can be perfectly eliminated.